Association between serum progesterone levels on the day of embryo transfer and clinical pregnancy outcomes in POSEIDON Group 1 patients.

OBJECTIVE

To investigate the relationship between serum progesterone (P) on the day of embryo transfer (ET) and pregnancy outcomes in patients classified as POSEIDON Group 1.

METHODS

This retrospective cohort study was conducted at the Reproductive Center of Yantai Yuhuangding Hospital between January 2016 and December 2023, enrolling 402 patients undergoing single or double ET on day 3 or day 5. Serum P and estradiol (E2) were measured on the day of ET, with clinical pregnancy rate as the primary outcome. Patients were stratified into three groups based on the 10th and 90th percentiles of serum P. Categorical variables were compared using the Pearson chi-square test or Fisher's exact test, continuous variables using Student's t-test, and multiple quantitative data using one-way analysis of variance. Multivariate logistic regression was performed to adjust for potential confounders. Additionally, sensitivity analysis and a robustness test based on body mass index (BMI) stratification were conducted.

RESULTS

The 10th and 90th percentiles of serum P on the day of ET were 9.45 ng/mL and 23.32 ng/mL, respectively. The clinical pregnancy rate was highest in the 9.45-23.32 ng/mL group and decreased significantly when serum P exceeded 23.32 ng/mL. After adjusting for confounders, multivariate logistic regression demonstrated that high serum P (≥23.32 ng/mL) was independently associated with a lower clinical pregnancy rate (adjusted OR = 1.454, 95% CI: 1.032-2.048, P = 0.032). Sensitivity analysis confirmed the robustness of this association. BMI stratification revealed that elevated serum P was associated with a reduced clinical pregnancy rate in normal-weight patients, but not in overweight/obese patients, with a significant interaction between serum P and BMI.

CONCLUSIONS

Serum P on the day of ET was significantly associated with clinical pregnancy rate in POSEIDON Group 1 patients, and BMI significantly modified this association. High serum P was linked to a lower clinical pregnancy rate in normal-weight patients, but not in overweight/obese patients. These findings support the implementation of individualized luteal support strategies based on serum P and BMI stratification.